The present invention relates to management of instructions in a processing core and, more particularly, to management of load instructions when dependencies are predicted with reference to older store instructions.
In out of order execution systems, it often is useful to predict the outcome of certain instructions before they have been executed. In the context of load instructions, prediction of dependencies between load instructions and previously-received store instructions can conserve processing resources. Execution of the load instruction should be deferred until after the store instruction executes. If the load instruction executed first, it would acquire invalid data. Thereafter, all instructions that are dependent upon the load instruction also would be permitted to execute, again with invalid data. Later, the core would cause the load instruction and all those instructions that are dependent on the load instruction to re-execute, possibly multiple times. The processing resources that were spent to execute and possibly re-execute the load instruction would be wasted. Other instructions could have been executed instead, yielding useful results. This phenomenon is explained in greater detail in a co-pending application Ser. No. 09/964,807, filed Sep. 28, 2001, and assigned to Intel Corp.
The present application proposes an implementation scheme to detect dependencies among load instructions and store instructions and to manage these instructions as they are processed by a core execution unit.